WARNING ! For those who have a TI-83 Premium CE or a TI-84 Plus CE (Python Edition or not), think very carefully before updating to OS 5.5.
While there are lots of Python-related improvements, this version removes ASM support. Most games, and some programs, will not work anymore.

Today, I will present the first circuit that I realized with this board.Later, may follow other more advanced montages combining this board with others to achieve advanced features: bj:

I want to point out that the purpose of this series of articles is not to do an electronics course, but to stir your interest in this fascinating and future-oriented discipline : p I stay available in comment section to answer more technical details

To begin, I wanted to start with a subject that you probably know:

the FM modulation

. OK, this name may not tell you much, but if I tell you

"FM Radio"

, I'm sure you see what I'm talking about!This is simply the

radio

that you can listen at home, with

your smartphone, your radio ...

FM means

"Frequency modulation"

(opposed to "AM" for "amplitude modulation", even if there are other types of modulation)

.Let's take a very simple example: a radio host will speak in a microphone. A system, called

VCO

for

Voltage Controlled Oscillator

, will generate a

sinusoidal signal whose frequency will vary according to the intensity of the voice of the host

. This signal will then be

amplified

, and switched to high frequency

(with a mixer)

to allow its transmission.The term of

frequency modulation

then makes sense!

Then, what your radio receiver does, it just

read the frequency modulated signal

, and retrieve the signal behind it with a fairly simple circuit.

I have already made a FM transmitter / receiver, if the subject interests you, I can develop it in a future article.

The question that interests us here, is how does this famous VCO work?

Generally, we don't use a VCO alone, it's always accompanied by a

system

to stabilize the central frequency [/b] and to keep the desired frequency using from one of the following circuits:

With a

PLL

, or Phase Lock Loop. It's the most used, but the most complex to treat. There are several types of PLL, we will deal here with the simplest case;

With a

quartz

. It's very accurate and durable, but cumbersome

(impossible to miniaturize on maps)

.

OK, now that you know what I'm talking about, how to realize a VCO concretely, and more specifically on the board

Analog System Labkit Pro

from

Texas Instruments

?

On our kit, we have at our disposal:

operational amplifiers

(AOP)

;

a linear voltage regulator;

potentiometers;

analog multipliers;

and analog-to-digital converters.

To realize our

first VCO

, we will simply use

operational amplifiers

and

potentiometers

.

Note that it's perfectly possible to realize a VCO using other components

(like transistors)

, as on this diagram, which I used in another project at school:

Show/Hide spoilerAfficher/Masquer le spoiler

In input

, we will have

a DC voltage

,

the modulating signal of our VCO

. The higher this voltage is, the higher the

frequency

output

high

. On the other hand, the lower the voltage is, the lower the signal will be

low frequency

. I chose to take a continuous voltage for simplicity's sake, but replace this voltage by the signal of a microphone, and the result will be the same, after amplification.This voltage will be modifiable using a potentiometer.

At the output

, there will be a loudspeaker allowing us to hear

the frequency modulated signal

. The higher the sound, the higher the frequency.

We will use 2 AOP, reference TL082, cascaded. AOPs are a kind of magic component, to amplify a signal, to create mathematical functions

(yes, of course!)

, to build filters ... They are simple to use and very practical in electronic, although they have many defects

(especially in high frequency!) [/​​i].

Here's what they will serve here:

The first

AOP

will be used to generate a square signal,

all or nothing

[i] (0 or 1)

, frequency modulated. This circuit is called a

Schmitt trigger

;

The second AOP

, mounted in

integrator

, will be used to generate a

frequency modulated triangular signal

.

An analog multiplier will be used to combine the two and create a so-called "linear" VCO by looping the system back.

The different components were calculated to be able to generate an audible frequency, between

50Hz and 2kHz

.In addition, connecting the speaker, with an impedance of 8 Ohms, will have almost no impact on global circuit, the output impedance of the AOP is very low. Nevertheless, to perfect the circuit, it would have been necessary to add a follower circuit between the VCO and the loudspeaker.

The

Analog System Labkit Pro

board will be powered by 2 laboratory generators, allowing 2 stable DC voltages to be generated. It's necessary to generate

+ 10V and -10V

.

Here are pictures of the complete circuit:

(click on images to enlarge them)

Now, let's listen to the sweet signal generated by this circuit. On the following video, I change the signal frequency by changing the value of the modulation voltage using the potentiometer. The generated sound is quite special

(even very strange: p)

, it comes from the generated signal, the speaker, and the video that distorts the sound. Sounds like a motor sound, but it's the speaker: pBut the most important is that the principle of frequency modulation works It would be possible to improve the signal by putting a filter.

(Only small problem: unfortunately I don't have any oscilloscope at home for the moment, I can unfortunately not see the shape of the signal !

Now, VCO and frequency modulation have no secrets for you: p! I also specify that the VCO is not only used in frequency modulation. You find it in analog-to-digital converters type Sigma-Delta or in Class D amplifiers.

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